In a conventional optical holographic technology, a portion of a coherent beam is used to irradiate to an object, and the reflected light from the object or the light transmitted through the object is incident to a holographic plate. This light is called as an object beam. Another portion of the coherent beam is projected onto the holographic plate to be used as a reference beam. Since the object beam and the reference beam are from the same coherent beam, the object beam and the reference beam are interfered with each other at the holographic plate to result in many bright and dark interference fringes. The interference pattern recorded on the holographic plate is formed as a hologram. The shape of the interference pattern indicates the phase relationship between the object beam and the reference beam. The bright/dark contrast level of the interference pattern indicates the intensity relationship between the object beam and the reference beam.
Conventionally, a disk-type multiplex holographic system uses a cylindrical lens to generate holograms. Due to the cylindrical lens, the hologram obtained at each shot is a long thin fan-shaped segment. Since the reconstructed image viewed by the observer is the combination of the images that are reconstructed from many segments, the reconstructed image is usually suffered from distortion. Moreover, numerous vertical dark lines are superimposed on the reconstructed image, which is referred as a picket-fence effect.
Moreover, in comparison with the conventional disk-type multiplex holographic system, a conventional image-plane disk-type multiplex holographic system utilizes a simplified optical system without cylindrical lens. By multiple exposures, the object image is recorded on a holographic film. However, due to the multiple exposures of the film, the brightness of the reconstructed image is possibly insufficient. Under this circumstance, the holographic image is not aesthetically pleasing, and it is difficult to produce a large-sized reconstructed image.
Moreover, a multi-color photographic hologram device and a light bias compensation device have been disclosed in Taiwanese Patent Publication No. M390525. In this literature, the diffraction angles of the green image and the blue image recorded on the film are changed by adjusting the incident angle of the reference light wave. Consequently, during the image reconstructing process, the biases of the projection angles of the green image and the blue image are corrected.
Therefore, there is a need of providing an approach to improve the size, brightness and color effects of the reconstructed image.